How Parallel Hydraulic Hybrid Vehicles Work

In a parallel hydraulic hybrid vehicle (HHV), the engine
still provides power to the wheels through a standard transmission. The hydraulic components are attached to the
driveshaft and assist in stopping and accelerating the vehicle. There are four main modes of operation in a parallel HHV :

Regenerative Braking

When a parallel HHV brakes the pump/motor is activated and (acting as a pump)
uses the rotating energy from the wheels to pump fluid from the low pressure reservoir
and transfer it into the high pressure accumulator for later use.
This spares the friction brakes from being used to stop the vehicle. The image at right provides a simple visual of this process.

Light Acceleration

When a parallel HHV needs to accelerate at moderate speeds only the pump/motor(acting as a motor) provides power to the driveshaft. This process spares the engine from having to burn as much fuel
to accelerate the vehicle. The image at right provides a simple visual of this process.

Extended Acceleration

When a parallel HHV is undergoing a heavy or extended acceleration the pump-motor (acting as a motor)
provides power to the driveshaft, but power from the engine is also added.
This process reduces the amount of engine power needed to accelerate powerfully
and quickly thereby saving fuel.The image at right provides a simple visual of this process.